Corrosion is one of the primary preventable causes of failure in transmission pipelines. Protective coatings serve as the first barrier against this phenomenon. Once a coating is compromised, it is only a matter of time before corrosion begins.
The Magnetic-Flux Leakage (MFL) method is currently the dominant technology for the in-line inspection (ILI) of transmission pipeline. Because the MFL ILI method depends on the ferrous nature of the material being inspected, it is only capable of detecting the effect of the corrosion problem and not the cause; a failure of the protective coating. Furthermore, MFL methods can potentially miss crack-like defects and have a large tolerance and low certainty for sizing metal-loss defects, such as corrosion.
The ability to reliably detect coating disbonds would represent a significant contribution to the pipeline integrity management sector as it would enable preventative maintenance action prior to the development of corrosive metal loss defects. In the event that defects are already present, a method of reliably detecting cracking and more accurately sizing metal-loss defects would also be a welcome contribution.
To prevent the onset of corrosion and to identify critical regions where corrosion may have already initiated, there is a need for a reliable, robust, multi-feature coating disbond detection technique that is applicable over a range of coating types and thicknesses. For regions that already contain defects, there is a present need for more accurate detection and sizing capabilities.
Furthermore, there is a need for a coating disbond detection technique and apparatus that will not be confounded by moderate wall thinning, diametral variations, and wetted/soiled coating interfaces and for a defect sizing technique that is highly sensitive to wall losses and cracking.
Furthermore, there is a need for a sensor arrangement and data acquisition technique that is relatively low cost and capable of withstanding the rigors encountered in an ILI environment.